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Orbital Defects : Hypertelorism and Hypotelorism
Introduction
Orbits can be identified from 10 to 12 weeks of gestation by transvaginal ultrasound. On ultrasound evaluation, orbits appear as echolucent circles, and inside these structures lenses can be indentified as small echogenic circular structures. In normal development, ocular structures develop laterally and migrate toward the midline to reach their final position. Orbital defects are rarely diagnosed in the fetus. However, these anomalies are highly associated with chromosomal and nonchromosomal defects.
Hypertelorism
Definition
Hypertelorism is defined by an increased interocular distance (IOD) above the 95th centile.
Prevalence and Epidemiology
This is a very rare condition.
Etiology and Pathophysiology
Three different mechanisms have been proposed to be responsible for this anomaly: (1) primary arrest of the migration process, (2) secondary arrest of migration due to the presence of a midline tumor, which mechanically limits migration, and (3) abnormal development and growth of the cranial bones.
Manifestations of Disease
Clinical Presentation
Hypertelorism is rarely associated with chromosomal abnormalities, but is highly associated with nonchromosomal syndromes, mainly in the face, central nervous system (CNS), or cranial bones. Some syndromes detectable in utero are listed in Table 66.1 . Isolated hypertelorism is very rare; therefore an anatomic scan and karyotype analysis are necessary in order to detect malformations or chromosomal abnormalities. The prognosis depends on the underlying syndrome or associated anomalies.
TABLE 66.1
NONCHROMOSOMAL SYNDROMES ASSOCIATED WITH HYPERTELORISM
| Hypertelorism associated with: | Syndrome |
|---|---|
| Anterior cephalocele, median cleft lip, and bifid nose | Frontonasal dysplasia |
| Turricephaly, macroglossia, syndactyly, fusion of cervical vertebrae, renal anomalies, and heart anomalies | Apert syndrome |
| Cataract, microcephaly, agenesis of the corpus callosum, severe cerebellar hypoplasia, micrognathia, short limbs, syndactyly, joint contractures, early-onset fetal growth retardation, and polyhydramnios | Neu-Laxova syndrome |
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